Hazard detection systems such as smoke-detection systems and carbon-monoxide detection systems are commonly used in homes and commercial buildings as these systems can provide an early warning of a hazardous condition, typically a fire, and can avoid serious bodily injury and/or may save lives. Such warning can be provided even sooner by directly detecting fire, e.g., by detecting a flame. Some heat-sensing based flame-detection techniques can be significantly costly and, hence, wide-scale use thereof is not highly likely.
Some cost-effective techniques that employ image processing for flame detection perform flicker detection. In general, a flicker detection system captures a series of images of a scene enabling detection of motion in the captured scene. The system then filters out motion at a certain range of frequencies, i.e., image data changing at a rate within a specified range, e.g., between 1.25 Hz and 4 Hz. Motion within this range is considered to be related to the flicker of a flame. Therefore, further analysis of the filtered and extracted data can lead to flame detection. Flicker detection systems can be highly inaccurate as they tend to exhibit a large false positive error, i.e., they often falsely determine the presence of a flame when none is present in the scene.
Reasons for false detection include presence of moving objects that are not flames, and changes in illumination. Typical examples include CRT displays and rotating lights of emergency vehicles, within the field of view. Detection systems may have poor sensitivity to flames when light levels are so low that the intensity of the light from the flame can result in a glowing white pulsating blob rather than a clearly defined flame. This can occur if the camera has adjusted its sensitivity to accommodate for the overall the low light conditions, resulting in any flame in a small area of the scene rapidly saturating within the image. Thus, for reliable flame detection, improved methods and systems that are both accurate and cost effective, are needed.